The present invention relates to brake resurfacers. In particular, the invention relates to a method and apparatus for resurfacing a braking surface of a vehicle brake rotor or drum while the brake rotor or drum is mounted to the vehicle.
Brake rotors and drums provide braking surfaces against which brake pads and brake shoes, respectively, frictionally engage to brake a vehicle. Ideally, brake rotors should rotate perpendicularly to the established axis without tolerance. Brake drums should rotate concentrically to the established axis without tolerance. In addition, the braking surfaces of brake rotors should be parallel to the caliper brake pad locating surfaces and the face of the hydraulic plunger.
During braking, it is also important that the brake pads and brake shoes "track" perfectly on the braking surfaces of the brake rotors and brake drums, respectively, without lateral movement. Lateral movement or "skating" of the brake pads and brake shoes with respect to the braking surfaces creates undesirable vibration and noise.
In an attempt to address this problem, products and servicing procedures have been developed to stabilize the brake pad and the brake shoe with respect to the caliper bracket and the back plate, respectively. One such servicing procedure involves applying a liquid adhesive to the back of the brake pad. The adhesive then solidifies between the brake pad backing plate and the caliper bracket to minimize lateral movement of the brake pads.
In another attempt to solve the skating problem, an adhesive backed aluminum sheet is secured between backing plates of the braking pads and the caliper brackets. The aluminum sheets provide a soft surface in which depressions outlining the shape of the caliper brackets form. The depressions minimize movement and stabilize the brake pads. Both attempts to solve the skating problem lose their effectiveness over time as the adhesives and the depressions break down or wear away. Moreover, both attempted solutions require additional servicing procedures and products which are time consuming and costly.
Excessive wear during use of the vehicle causes the braking surface of brake rotors and drums to wear unevenly, and generates heat, causing warping in the braking surface. As a result, brake rotors and drums do not rotate perpendicularly and concentrically, respectively, to the established axis. These errors, or tolerances, are known as run out, flatness, parallelism and perpendicularity. They are the source of many objectionable problems.
In such cases, the braking surface must be resurfaced or, if beyond specified tolerances, replaced. Previously, resurfacing of the brake rotor has been accomplished with a lathe-type resurfacing tool. With a lathe-type resurfacing tool, cutter blades are moved laterally across the rotating braking surface to cut off a thin layer of the braking surface and expose a generally smooth, renewed braking surface. The renewed braking surface typically has a surface finish of about 40-80 microfinish and includes microscopic, non-concentric grooves. As the cutter blades move laterally across the rotating braking surface, the microscopic grooves are created in the braking surface. These grooves form a lead angle created by the laterally moving cutter blade. As a whole, the series of grooves interconnected by the lead angle spiral towards the center of the brake rotor or the inner edge of the brake drum.
Lathe resurfacing tools are expensive and require careful adjustment. Even a slight misadjustment of the cutter head can cause damage to the braking surface of the rotor or drum. Furthermore, the extreme pressure created by engaging the very small surface of the cutter head against the braking surface requires very heavy duty ways and bracing. In addition, this device may require multiple passes across the braking surface with the cutter blade to remove a layer of sufficient thickness so as to achieve a smooth braking surface. As a result, a standard cutting thickness is normally chosen to reduce the number of passes across the braking surface. Although time is saved by decreasing the number of passes required to achieve a smooth braking surface, the standard cutting depth is often excessive, reducing the life span of the rotor or drum.
To solve some of these problems, a grinder resurfacing tool has been used to resurface the braking surface of a vehicle brake rotor. These devices employ grinding stones or chocks which are formed from multiple layers of abrasive particles bonded together. As the stones contact the braking surface, layers of the abrasive particles as well as the removed braking surface material flake away to expose new layers of abrasive particles. Because abrasive particles flake away with the removed braking surface material, removed braking surface material does not plug the grinding surface. As a result, the grinding stones are capable of resurfacing multiple braking surfaces.
Furthermore, because it is believed that a smooth, polished braking surface is desirable to prevent excessive wear of the brake pad or brake shoe and to prolong useful life of each brake pad and brake shoe, the grinding stones are designed to create a smooth, polished braking surface. Because the abrasive particles or grits on each layer are randomly positioned with respect to abrasive particles on adjacent layers, any peaks created in the braking surface by one layer of abrasive particles will be cut away by the next exposed adjacent layer of abrasive particles to establish a generally smooth, polished braking surface. However, because new abrasive material or new layers of abrasive particles are continually exposed, the grinding stones also create an ever changing uncontrollable polished surface condition on the braking surface. Consequently, any grooves created in the surface are deminimus and are not generally concentric. The grinding stones are typically mounted in an independent rotational device so as to polish off the worn surface as both the brake rotor and the grinding stones rotate relative to each other about dissimilar axes of rotation.
Previously, the braking surface of brake rotors and brake drums has been resurfaced on independent resurfacing devices using either cutting blades or grinding stones. With independent resurfacing devices, the brake rotor or drum must be dismounted from the vehicle to resurface the braking surface of the brake rotor. Such procedures involve disassembling the rotor or the drum; securing the rotor or drum to an independent resurfacing device such as a turning machine; machining or resurfacing the braking surface; and reassembling the rotor or drum to the vehicle. This procedure is time-consuming, costly and requires great skill and expertise. As a result, many vehicle owners put off necessary brake resurfacing because of the cost and the inconvenience of having their vehicle tied up during brake resurfacing.
Moreover, these methods do not entirely achieve a preferred end result. Because the rotor or drum must be disassembled from its original assembly to be placed upon an independent machine, the rotor or drum will not be returned to its identical position upon reassembly. Upon reassembly of the rotors and drums, any accumulated errors or misalignment causes vibration and other objectionable results.
To reduce some of the time required for brake resurfacing and to improve resurfacing results, brake resurfacing devices have been adapted to resurface brake rotors without removing the rotors from the vehicle. Typically, the device is mounted to the wheel hub, wheel shaft, or any other convenient member of the vehicle. The cutting blade or the grinding stone of the mounted resurfacer is typically supported by the mounted resurfacing device itself. The resurfacing device positions and aligns either the cutting blades or the grinding stones against the braking surface of the rotor or drum to resurface the braking surface. As a result, brake resurfacing accuracy is dependent upon proper mounting of the resurfacing device. To properly mount the resurfacing device requires careful adjustment. Such adjustment is time consuming and costly.
With both independent and mounted resurfacing devices, the cutter blades or the grinding stones are carried or supported by the device itself. In addition, the device itself positions the cutting blades or the grinding stones against the rotor or drum surface to be resurfaced. Because the device itself supports and positions either the cutting blades or the grinder stones against the braking surface, this device requires exacting alignment and adjustment to insure that the braking surface is resurfaced correctly to minimize or eliminate error or tolerance. This alignment is often time consuming, costly and prone to mechanic error.
Moreover, despite careful adjustment, both devices still result in imperfect brake resurfacing. Because both the independent and mounted resurfacing devices position the cutting blades or the grinder stones against the rotor or drum braking surface, the particular idiosyncracies of the devices are machined into the braking surface of the rotor or drum. These idiosyncracies, otherwise known as composite errors, include accumulated manufacturing tolerances and wear upon the resurfacing devices over time. These composite errors, which are machined into the braking surface, prevent rotor surfaces from being parallel to the caliper brake pad locating surfaces and the face of the hydraulic plunger and also prevent brake drums from rotating concentrically to the established axis without tolerance.
Cost is another major disadvantage to these methods for resurfacing braking surfaces. Both methods require expensive independent or mounted resurfacing devices.